linux-kernel - [PATCH 5.15 545/667] ext4: filter out EXT4_FC_REPLAY from on-disk superblock field s

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Message-Id: <20220607164951.045941234@linuxfoundation.org>
Date:   Tue,  7 Jun 2022 19:03:30 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, stable@...nel.org,
        Theodore Tso <tytso@....edu>,
        syzbot+c7358a3cd05ee786eb31@...kaller.appspotmail.com
Subject: [PATCH 5.15 545/667] ext4: filter out EXT4_FC_REPLAY from on-disk superblock field s_state

From: Theodore Ts'o <tytso@....edu>

commit c878bea3c9d724ddfa05a813f30de3d25a0ba83f upstream.

The EXT4_FC_REPLAY bit in sbi->s_mount_state is used to indicate that
we are in the middle of replay the fast commit journal.  This was
actually a mistake, since the sbi->s_mount_info is initialized from
es->s_state.  Arguably s_mount_state is misleadingly named, but the
name is historical --- s_mount_state and s_state dates back to ext2.

What should have been used is the ext4_{set,clear,test}_mount_flag()
inline functions, which sets EXT4_MF_* bits in sbi->s_mount_flags.

The problem with using EXT4_FC_REPLAY is that a maliciously corrupted
superblock could result in EXT4_FC_REPLAY getting set in
s_mount_state.  This bypasses some sanity checks, and this can trigger
a BUG() in ext4_es_cache_extent().  As a easy-to-backport-fix, filter
out the EXT4_FC_REPLAY bit for now.  We should eventually transition
away from EXT4_FC_REPLAY to something like EXT4_MF_REPLAY.

Cc: stable@...nel.org
Signed-off-by: Theodore Ts'o <tytso@....edu>
Link: https://lore.kernel.org/r/20220420192312.1655305-1-phind.uet@gmail.com
Link: https://lore.kernel.org/r/20220517174028.942119-1-tytso@mit.edu
Reported-by: syzbot+c7358a3cd05ee786eb31@...kaller.appspotmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 fs/ext4/super.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -4391,7 +4391,7 @@ static int ext4_fill_super(struct super_
 					sbi->s_inodes_per_block;
 	sbi->s_desc_per_block = blocksize / EXT4_DESC_SIZE(sb);
 	sbi->s_sbh = bh;
-	sbi->s_mount_state = le16_to_cpu(es->s_state);
+	sbi->s_mount_state = le16_to_cpu(es->s_state) & ~EXT4_FC_REPLAY;
 	sbi->s_addr_per_block_bits = ilog2(EXT4_ADDR_PER_BLOCK(sb));
 	sbi->s_desc_per_block_bits = ilog2(EXT4_DESC_PER_BLOCK(sb));

@@ -5937,7 +5937,8 @@ static int ext4_remount(struct super_blo
 				if (err)
 					goto restore_opts;
 			}
-			sbi->s_mount_state = le16_to_cpu(es->s_state);
+			sbi->s_mount_state = (le16_to_cpu(es->s_state) &
+					      ~EXT4_FC_REPLAY);

 			err = ext4_setup_super(sb, es, 0);
 			if (err)